The present invention relates to the field of Asynchronous Transfer Mode (ATM) networks and more particularly to a signaling method for rerouting ATM connections within the Private Network Node Interface or Private Network-to-Network Interface (PNNI) domain.
Developed through the efforts of the ATM Forum and detailed in "The ATM Forum Technical Committee, Private Network-Network Interface Specification Version 1.0 (PNNI 1.0)," af-pnni-0055.000, March 1996, PNNI 1.0 is a protocol standard that enables the building of multivendor, interoperable ATM switching networks. The protocol allows for the building and maintenance of large ATM networks because it provides hierarchical, dynamic link-state routing instructions and communication pathways. The protocol permits separate ATM switches within interconnecting networks to continuously communicate and share information. In addition, PNNI defines signaling requests for establishing and taking down point-to-point and point-to-multipoint connections across those networks.
PNNI routing is based on well-known, link-state routing techniques similar to, for example, Open Shortest Path First (OSPF). In addition to the basic link-state mechanism, PNNI provides support for quality of service (QoS) routing, required for applications with real-time requirements and scalability to large global networks. These features provide large- scale networks with a single routing protocol, unlike the Internet strategy of using a number of protocols at various levels.
In these environments, rerouting refers to changing the path of an existing connection anywhere between its two end-points. No user signaling is needed to reestablish the connection as the operation is performed by the network, allowing the calling and called parties to be continuously connected. To establish these connections, PNNI environments operate with peer groups (PG), a collection of logical nodes that exchange information with other members of the group. This information exchange allows all members of the same peer group to maintain an identical view of the PG and for those nodes outside of the PG to exchange messages with the PG as a whole.
PNNI 1.0 does not support rerouting after a connection has been established. One submission to the ATM Forum, entitled Signaling Procedures For Fault Tolerant Connections AF/97-0391R1 by D. M. Kushi et al. and E. M. Spiegel (April 1997), however, discussed so-called fault-tolerant connections. According to AF/97-0391, which is herein incorporated by reference, these connections are automatically reestablished (without user intervention) only in the case of a network failure. When a failure occurs, the fault-tolerant connection is rerouted end-to-end, within the PNNI domain, i.e., between the two user-to-network interfaces (UNI) connecting the calling and called party.
End-to-end and fault-based rerouting schemes are restrictive because they must essentially reestablish the entire connection and as a result, are slower than partial connection rerouting. Therefore, a need exists for a rerouting solution that overcomes the deficiencies of fault tolerant and end-to-end rerouting. The solution should provide a more generic and complete mechanism and protocol that permits connection rerouting for reasons beyond network failures. Path optimization, load balancing, fault tolerance, call priority, etc. should be among the features supported by any PNNI rerouting solution. These rerouting reasons could be considered value added features, providing users of the network with a variety of increased services and potentially better quality connection paths. Fundamental to a generic connection rerouting solution is the ability of the connections to be rerouted along a new path prior to releasing an old path's connection. Finally, the solution should interface with the existing PNNI routing protocols that do not support basic rerouting functions, namely PNNI 1.0.